JP2017111431A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming apparatus which can correct gray levels with high accuracy.SOLUTION: An image forming apparatus includes a toner-image forming unit, an information acquisition unit, and a control unit. The control unit executes processing (i) and processing (ii). In the processing (i), the control section controls the toner-image forming unit to form at least one of a single-dot toner image, and a toner-image including a dot line formed by arranging single dots in one or a plurality of lines in a predetermined direction, as a test image, and causes the information acquisition unit to acquire optical information of the formed test image. In the processing (ii), the control section corrects toner-image forming condition (exposure condition or transfer condition) in the toner-image forming unit, on the basis of a state (size, density distribution, and edge shape) of the test image obtained from the optical information acquired by the information acquisition unit.SELECTED DRAWING: Figure 3

Description

  The present invention relates to an image forming apparatus, and more particularly to an image quality adjustment technique applied to an electrophotographic image forming apparatus.

  In an electrophotographic image forming apparatus, the value of a control parameter is set in advance for each gradation of each color constituting a predetermined color space (for example, CMYK color space) so that a desired image quality can be obtained. On the other hand, even if the image forming apparatus is controlled with the same control parameter value, the gradation changes due to changes in the environment (temperature, humidity, etc.) or aging of the apparatus, and the desired gradation is reproduced. Can be difficult.

  For this reason, various techniques for correcting the gradation have been conventionally proposed (see, for example, Patent Document 1). For tone correction, a test pattern that indicates a change in density of each color is usually used. Here, the density change is often expressed by a halftone dot or a dot line. Then, the value of the control parameter is corrected based on the density change of each color indicated in the test pattern so that the desired gradation is reproduced.

JP 2004-179768 A

  However, there is a problem that even the patches representing the same gradation of the same color in the test pattern cannot always reproduce the same density. And the main cause is that the reproducibility of the state of size, density distribution, edge shape, etc. is reduced in a single dot or dot line. For this reason, it has been difficult to realize gradation correction with high accuracy by the conventional technique.

  SUMMARY OF THE INVENTION An object of the present invention is to provide an image forming apparatus that enables gradation correction with high accuracy.

  A first image forming apparatus according to the present invention includes a toner image forming unit, an information acquisition unit, and a control unit. The toner image forming unit includes an exposure unit that forms an electrostatic latent image on an image carrier, a developing unit that visualizes the electrostatic latent image to form a toner image, and a transfer roller that transfers the toner image to a transfer belt. Including. The information acquisition unit acquires the optical information of the toner image after the transfer of the toner image onto the transfer belt and before the toner image is fixed on the paper. And a control part performs processing (i) and (ii). That is, in the process (i), the control unit includes at least one of a single-dot toner image and a dot-line toner image in which a single dot is arranged in one or more rows in a predetermined direction. One of them is formed as a test image, and optical information of the formed test image is acquired by the information acquisition unit. In the process (ii), the control unit corrects the toner image forming condition in the toner image forming unit based on the state of the test image obtained from the optical information acquired by the information acquiring unit.

  According to the image forming apparatus, the state of the test image that is a single dot or a dot line is corrected, so that the reproducibility of the state is increased. Therefore, the reproducibility of the change in the density of each color is enhanced when forming a test pattern used for tone correction.

  In the image forming apparatus, the state of the test image preferably includes at least one of size, density distribution, and edge shape.

  In the image forming apparatus, it is preferable that the control unit further executes processes (iii) and (iv). That is, in the process (iii), the control unit detects from the optical information acquired by the information acquisition unit the presence or absence of toner scattering marks that may be generated when the test image is transferred to the transfer belt. In the process (iv), the control unit corrects the conditions for the transfer by the transfer roller as necessary based on the detection result in the process (iii).

  According to the above configuration, toner scattering that may occur when the test image is transferred to the intermediate belt is suppressed. Therefore, in the image forming apparatus, the influence of the scattering marks on the correction process executed by the control unit is removed, and as a result, the correction process with high accuracy is realized.

  In the image forming apparatus, the control unit may cause the toner image forming unit to form a test image at each of a plurality of different positions in the width direction of the transfer belt in the process (i). In this configuration, it is preferable that an information acquisition unit is provided corresponding to each of the plurality of positions. In the process (ii), it is preferable that the control unit corrects the toner image forming condition for each position by using the optical information of the test image at each position.

  According to the above configuration, variations in the state (size, density distribution, edge shape, etc.) of single dots or dot lines that can be caused by the difference in position in the width direction of the transfer belt are corrected.

  According to the image forming apparatus of the present invention, it is possible to perform gradation correction with high accuracy.

1 is a conceptual diagram illustrating a main part of an image forming apparatus according to an embodiment of the present invention. 1 is a block diagram of an image forming apparatus. It is the flowchart which showed the flow of the size correction process. It is the flowchart which showed the flow of density distribution correction processing. It is the flowchart which showed the flow of the edge shape correction process. It is the flowchart which showed the flow of the scattering suppression process. It is the top view which showed arrangement | positioning of the imaging part in other embodiment. It is the flowchart which showed the flow when size correction processing and density distribution correction processing were combined. It is the flowchart which showed the flow when size correction processing and edge shape correction processing were combined.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

[1] First Embodiment [1-1] Configuration of Image Forming Apparatus As shown in FIGS. 1 and 2, the image forming apparatus performs electrophotographic image forming processing based on image data, thereby forming a sheet. Print an image on Z. Specifically, the image forming apparatus includes four toner image forming units 1, an intermediate transfer belt 2, a secondary transfer roller 3, a fixing unit 4, an imaging unit 5, a storage unit 6, and a control unit 7 as main parts thereof. Is provided.

<Toner image forming unit>
In the image forming apparatus of this embodiment, a CMYK space is adopted as a color space to be used. The four toner image forming units 1 respectively form toner images of four colors (cyan, magenta, yellow, and black) constituting the CMYK space. Note that the number of installed toner image forming units 1 may be changed according to the color space to be used. For example, in the case of a monochrome image forming apparatus, there is one toner image forming unit 1.

  Each of the toner image forming units 1 includes a photosensitive drum 11, a charging unit 12, an exposure unit 13, a developing unit 14, a primary transfer roller 15, and a cleaning unit 16.

  The photosensitive drum 11 is an electrostatic latent image carrier. The charging unit 12 charges the photosensitive drum 11 so that the potential of the peripheral surface thereof becomes a predetermined potential. The exposure unit 13 forms an electrostatic latent image corresponding to the image data by irradiating the charged peripheral surface of the photosensitive drum 11 with a laser L.

  The developing unit 14 visualizes the electrostatic latent image formed on the peripheral surface of the photosensitive drum 11 to form a toner image. Specifically, the developing unit 14 applies a bias (development bias) to the developing roller to move the toner attached to the peripheral surface of the developing roller to the peripheral surface of the photosensitive drum 11 at the development position. Let Thereby, the electrostatic latent image is visualized and a toner image is formed. The formed toner image is conveyed to the position where the transfer (primary transfer) to the intermediate transfer belt 2 is executed by the rotation of the photosensitive drum 11.

  The primary transfer roller 15 transfers the toner image carried on the photosensitive drum 11 to the intermediate transfer belt 2. Specifically, the primary transfer roller 15 applies a bias (transfer bias) to itself to generate an electrostatic force on the toner constituting the toner image, and uses the electrostatic force to generate the toner image. Move to the intermediate transfer belt 2.

  The four color toner images respectively formed by the four toner image forming units 1 based on the image data are transferred to the same area of the intermediate transfer belt 2 so as not to be shifted from each other. As a result, the four color toner images overlap, and a full color toner image is formed on the intermediate transfer belt 2. The full-color toner image is conveyed to a position where the transfer (secondary transfer) to the paper Z is executed by the rotation of the intermediate transfer belt 2.

  The cleaning unit 16 removes toner and other attached matters (dust, etc.) remaining on the peripheral surface of the photosensitive drum 11 after the primary transfer. Thereby, preparation for the next image forming process is performed.

<Secondary transfer roller>
The secondary transfer roller 3 transfers the full-color toner image carried on the intermediate transfer belt 2 to the paper Z. Specifically, the secondary transfer roller 3 applies a bias to itself to generate an electrostatic force on the toner constituting the toner image, and uses the electrostatic force to transfer the toner image to the paper Z. Move.

<Fixing part>
The fixing unit 4 includes a heating roller 41 and a pressure roller 42 pressed against the heating roller 41. The sheet Z on which the toner image has been transferred is passed between the heating roller 41 and the pressure roller 42, whereby appropriate heat and pressure are applied to the toner image. As a result, the toner image is fixed to the paper Z.

<Imaging unit>
The imaging unit 5 captures the toner image transferred to the intermediate transfer belt 2 to generate image data that is optical information of the toner image. In the present embodiment, in the image data obtained by the imaging, the imaging unit 5 has a high level so that the state (size, density distribution, edge shape, etc.) described later can be recognized. A resolution image sensor is used. More specifically, an image sensor having a resolution of four times or more based on the resolution of a single dot that can be formed by the toner image forming unit 1 is used as the imaging unit 5. For example, when the resolution of a single dot is 600 dpi, an image sensor having a resolution of 2400 dpi or higher is preferable as the imaging unit 5. The image pickup unit 5 is not limited to picking up the toner image transferred to the intermediate transfer belt 2, and picks up the toner image at any time after the transfer to the intermediate transfer belt 2 and until it is fixed on the paper. It may be a thing.

<Storage unit>
The storage unit 6 stores image data used for printing and set values of control parameters (laser L duty, development bias, transfer bias, etc.) used to control each unit (toner image forming unit 1 and the like) of the image forming apparatus. Is memorized.

<Control unit>
The control unit 7 controls each unit of the image forming apparatus based on the image data and setting values stored in the storage unit 6.

[1-2] Control of Image Forming Apparatus Next, details of control performed by the control unit 7 in the image forming apparatus will be described. In addition to performing normal printing processing, the control unit 7 performs gradation correction processing so that a desired image quality can be obtained in the printed matter. In the present embodiment, the control unit 7 further executes a size correction process to enable a gradation correction process with high accuracy. Details of the size correction process will be described below with reference to FIG.

  First, the control unit 7 causes each toner image forming unit 1 to form a single dot toner image as a test image (step S101). Next, the control unit 7 acquires the image data of the test image by causing the imaging unit 5 to capture the formed test image (step S102). At this time, the control unit 7 may acquire image data for each single dot of different colors formed in each of the four toner image forming units 1 or one image including all these single dots. Data may be acquired.

  However, no matter what the image data acquisition form is, the control unit 7 determines the toner image for each toner image forming unit 1 based on a single dot formed in the toner image forming unit 1. Correct the formation conditions. Therefore, hereinafter, the processing after step S103 will be described for one toner image forming unit 1 and a single dot formed by the toner image forming unit 1. The same applies to the processes described in the second and subsequent embodiments.

  After step S102, the control unit 7 calculates the size of a single dot from the acquired image data (step S103). Specifically, the control unit 7 extracts pixels constituting a single dot image from the image data, and counts the number of the constituent pixels, whereby the total number of constituent pixels (the number of pixels N1). Is calculated as the size of a single dot. At this time, the number of pixels corresponding to the width of a single dot in a predetermined direction (for example, the coordinate axis direction of the two-dimensional coordinate system set in the image data) may be calculated as the number of pixels N1.

  After step S103, the control unit 7 compares the number of pixels N1 (single dot size) with a predetermined number Nt1 (step S104). Here, the predetermined number Nt1 is a value of the number of pixels N1 set in advance as corresponding to an appropriate size of a single dot. Specifically, the control unit 7 determines whether the pixel number N1 is a value larger than the predetermined number Nt1, a value that matches the predetermined number Nt1, or a value smaller than the predetermined number Nt1. The predetermined number Nt1 of data is stored in the storage unit 6, for example, and the control unit 7 reads out the predetermined number Nt1 of data from the storage unit 6 as necessary.

  As an example, the control unit 7 determines whether the difference (N1−Nt1) between the number of pixels N1 and the predetermined number Nt1 is a value larger than the upper limit value of the predetermined range, a value within the predetermined range, or a value smaller than the lower limit value of the predetermined range. It is judged whether it is. Here, the predetermined range is a range in which it is recognized that the number of pixels N1 matches the predetermined number Nt1 within this range. The determination result that “the difference (N1−Nt1) is larger than the upper limit value of the predetermined range” corresponds to the determination result that “the pixel number N1 is larger than the predetermined number Nt1”. The determination result that “the difference (N1−Nt1) is a value within a predetermined range” corresponds to the determination result that “the number of pixels N1 is a value that matches the predetermined number Nt1”. The determination result that “the difference (N1−Nt1) is smaller than the lower limit value of the predetermined range” corresponds to the determination result that “the number of pixels N1 is smaller than the predetermined number Nt1”.

  Thereafter, the control unit 7 corrects the exposure conditions by the exposure unit 13 as necessary based on the comparison result in step S104 (steps S105 and S106). Specifically, when it is necessary to adjust the size of a single dot as a result of the comparison in step S104, the control unit 7 controls the power of the laser L output from the exposure unit 13 (for example, the peak output value or (Duty) is corrected. More specifically, it is as follows.

  When a comparison result with “the number of pixels N1 is larger than the predetermined number Nt1 (N1> Nt1)” is obtained in step S104, the control unit 7 sets the single dot size to an appropriate size. The power of the laser L is reduced (step S105). Thereafter, the control unit 7 returns to step S101.

  On the other hand, when a comparison result with “the number of pixels N1 is smaller than the predetermined number Nt1 (N1 <Nt1)” is obtained in step S104, the control unit 7 determines that the single dot size is an appropriate size. Thus, the power of the laser L is increased (step S106). Thereafter, the control unit 7 returns to step S101.

  When a comparison result with “the number of pixels N1 is a value that matches the predetermined number Nt1 (N1 = Nt1)” is obtained in step S104, the control unit 7 does not change the power of the laser L and does not change the power of step S107. Migrate to

  That is, in FIG. 3, steps S101 to S106 are repeatedly executed until a comparison result is obtained in step S104 that “the number of pixels N1 is a value matching the predetermined number Nt1 (N1 = Nt1)”. Note that the size correction process for a single dot is not limited to this. In step S104, “the number of pixels N1 is larger than the predetermined number Nt1 (N1> Nt1)” or “the number of pixels N1 is greater than the predetermined number Nt1. When a comparison result with “small value (N1 <Nt1)” is obtained, the correction process for decreasing or increasing the laser power may be performed, and then the process may return to step S107 without returning to step S101.

  In step S <b> 107, the control unit 7 forms dot lines (hereinafter simply referred to as “dot lines”) in which a single dot is arranged in one or more rows in a predetermined direction in each of the toner image forming units 1. A toner image is formed as a test image. Here, the predetermined direction is, for example, a main scanning direction or a sub-scanning direction. Next, the control unit 7 acquires image data of the test image by causing the imaging unit 5 to capture the formed test image (step S108). At this time, the control unit 7 may acquire image data for each dot line having a different color formed in each of the four toner image forming units 1, or one image data including all these dot lines. You may get it.

  However, regardless of the image data acquisition form, the control unit 7 forms the toner image for each toner image forming unit 1 based on the dot lines formed in the toner image forming unit 1. Correct the condition. Therefore, hereinafter, the processing after step S108 will be described with respect to one toner image forming unit 1 and the dot lines formed by the toner image forming unit 1. The same applies to the processes described in the second and subsequent embodiments.

  After step S107, the control unit 7 calculates the dot line width from the acquired image data (step S109). Specifically, the control unit 7 extracts the pixels constituting the dot line image from the image data and counts the number of constituent pixels in the width direction of the dot line. Thereby, the control unit 7 calculates the total number of constituent pixels in the width direction (number of pixels N2) as the size of the dot line.

  After step S109, the controller 7 compares the number of pixels N2 (dot line width) with a predetermined number Nt2 (step S110). Here, the predetermined number Nt2 is a value of the number of pixels N2 set in advance as corresponding to the appropriate width of the dot line. Specifically, the control unit 7 determines whether the pixel number N2 is a value larger than the predetermined number Nt2, a value that matches the predetermined number Nt2, or a value smaller than the predetermined number Nt2. The predetermined number Nt2 of data is stored in the storage unit 6, for example, and the control unit 7 reads the predetermined number Nt2 of data from the storage unit 6 as necessary.

  As an example, the control unit 7 determines whether the difference (N2−Nt2) between the number of pixels N2 and the predetermined number Nt2 is a value greater than the upper limit value of the predetermined range, a value within the predetermined range, or a value smaller than the lower limit value of the predetermined range. It is judged whether it is. Here, the predetermined range is a range in which the number of pixels N2 is recognized as matching the predetermined number Nt2 within this range. The determination result that “the difference (N2−Nt2) is larger than the upper limit value of the predetermined range” corresponds to the determination result that “the number of pixels N2 is larger than the predetermined number Nt2”. The determination result that “the difference (N2−Nt2) is a value within a predetermined range” corresponds to the determination result that “the number of pixels N2 is a value that matches the predetermined number Nt2.” The determination result that “the difference (N2−Nt2) is smaller than the lower limit value of the predetermined range” corresponds to the determination result that “the pixel number N2 is smaller than the predetermined number Nt2”.

  Thereafter, the control unit 7 corrects the conditions for exposure by the exposure unit 13 as necessary based on the comparison result in step S110 (steps S111 and S112). Specifically, when it is necessary to adjust the width of the dot line as a result of the comparison in step S110, the control unit 7 controls the power of the laser L output from the exposure unit 13 (for example, the peak output value or the duty). ) Is corrected. More specifically, it is as follows.

  When a comparison result with “the number of pixels N2 is larger than the predetermined number Nt2 (N2> Nt2)” is obtained in step S110, the control unit 7 makes the dot line width an appropriate width. The power of the laser L is reduced (step S111). Thereafter, the control unit 7 returns to Step S107.

  On the other hand, if a comparison result with “the pixel number N2 is smaller than the predetermined number Nt2 (N2 <Nt2)” is obtained in step S110, the control unit 7 sets the dot line width to an appropriate width. In the same manner, the power of the laser L is increased (step S112). Thereafter, the control unit 7 returns to Step S107.

  When a comparison result with “the number of pixels N2 is a value that matches the predetermined number Nt2 (N2 = Nt2)” is obtained in step S110, the control unit 7 corrects the size without changing the power of the laser L. The process ends, and the process proceeds to gradation correction processing.

  That is, in FIG. 3, steps S107 to S112 are repeatedly executed until a comparison result is obtained in step S110 that “the number of pixels N2 is a value that matches the predetermined number Nt2 (N2 = Nt2)”. Note that the size correction processing related to the dot line is not limited to this, and “the number of pixels N2 is larger than the predetermined number Nt2 (N2> Nt2)” or “the number of pixels N2 is smaller than the predetermined number Nt2 in step S110. When a comparison result with the value (N2 <Nt2) ”is obtained, the size correction process may be terminated without returning to step S107 after performing the correction process for decreasing or increasing the laser power.

  In the gradation correction process, the control unit 7 causes the toner image forming unit 1 to form a test pattern indicating the density change of each color. Then, the control unit 7 corrects the gradation of each color based on the density change indicated by the test pattern.

  According to the size correction process, the size of single dots or dot lines is corrected, so that the reproducibility of those sizes is enhanced. Therefore, the reproducibility of the change in the density of each color is enhanced when forming a test pattern used for tone correction. Therefore, according to the image forming apparatus of the first embodiment, gradation correction can be performed with high accuracy.

  Note that the processing of steps S101 to S106 and the processing of steps S107 to S112 are not limited to the case where both are executed as in the present embodiment, and only one of the processing may be executed as the size correction processing. Good.

  In addition, a single dot test image may be used in which a plurality of single dots are formed with one dot or a plurality of intervals between them, or at intervals. It may be arranged in a halftone dot shape. The dot line test image may include a plurality of dot lines formed at intervals of one line or a plurality of lines between them. As described above, by using a plurality of single dots or dot lines as a test image, it becomes easy to recognize single dots or dot lines in the image data. The same applies to various correction processes described in the embodiments described later.

  Further, by using a plurality of single dots or dot lines as a test image, the size to be compared with the predetermined number Nt1 or Nt2 is obtained from the plurality of single dots or dot lines in the size comparison in step S104 or S110. An average size can be used. Thereby, a size correction process in consideration of the size variation is possible.

[2] Second Embodiment The control unit 7 may execute density distribution correction processing instead of size correction processing in order to enable gradation correction processing with high accuracy. Details of the density distribution correction processing will be described below with reference to FIG. As described in the sixth embodiment, the density distribution correction process may be used in combination with the size correction process described above.

  In steps S201 and S202, the same processing as in steps S101 and S102 of the first embodiment is executed. After step S202, the control unit 7 detects a single dot density distribution from the acquired image data (step S203). Specifically, the control unit 7 extracts pixels constituting a single dot image from the image data, and based on the pixel value of the extracted pixels, the density D1 and the edge of the central portion of the single dot The density D2 of the part is calculated.

  After step S203, the control unit 7 compares the two densities D1 and D2 (step S204). Specifically, the control unit 7 determines whether the density D1 is a value greater than the density D2, a value matching the density D2, or a value smaller than the density D2.

  As an example, the controller 7 has a difference (D1−D2) between the two densities D1 and D2 that is a value larger than the upper limit value of the predetermined range, a value within the predetermined range, or a value smaller than the lower limit value of the predetermined range. Judge whether or not. Here, the predetermined range is a range in which the density D1 is recognized to match the density D2 within this range. The determination result that “difference (D1−D2) is larger than the upper limit value of the predetermined range” corresponds to the determination result that “density D1 is greater than density D2”. The determination result that “the difference (D1−D2) is a value within a predetermined range” corresponds to the determination result that “the density D1 is a value that matches the density D2.” The determination result that “difference (D1−D2) is smaller than the lower limit value of the predetermined range” corresponds to the determination result that “density D1 is smaller than density D2”.

  Thereafter, the control unit 7 corrects the transfer conditions by the primary transfer roller 15 as necessary based on the comparison result in step S204 (steps S205 and S206). Specifically, when it is necessary to adjust the density distribution of a single dot as a result of the comparison in step S204, the control unit 7 corrects the transfer bias and transfer pressure of the primary transfer roller 15. More specifically, it is as follows.

  When the comparison result “Density D1 is greater than density D2 (D1> D2)” is obtained in step S204, the control unit 7 sets the transfer bias so that the density of a single dot is uniform. Increase (step S205). Thereafter, the control unit 7 returns to step S201.

  On the other hand, when a comparison result with “Density D1 is smaller than density D2 (D1 <D2)” is obtained in step S204, the control unit 7 transfers the density so that the density of a single dot is uniform. The pressure is reduced (step S206). Thereafter, the control unit 7 returns to step S201.

  If a comparison result is obtained in step S204 that “density D1 is a value that matches density D2 (D1 = D2)”, control unit 7 proceeds to step S207 without changing the transfer bias and transfer pressure. Transition.

  In steps S207 and S208, the same processing as that in steps S107 and S108 of the first embodiment is executed. After step S208, the control unit 7 detects the density distribution of the dot lines from the acquired image data (step S209). Specifically, the control unit 7 extracts the pixels constituting the dot line image from the image data, and based on the pixel value of the extracted pixels, the density D3 of the central portion in the width direction of the dot line The density D4 of the edge portion is calculated.

  After step S209, the control unit 7 compares the two densities D3 and D4 (step S210). Specifically, the control unit 7 determines whether the density D3 is a value greater than the density D4, a value matching the density D4, or a value smaller than the density D4.

  As an example, the control unit 7 has a difference (D3−D4) between the two densities D3 and D4 that is a value larger than the upper limit value of the predetermined range, a value within the predetermined range, or a value smaller than the lower limit value of the predetermined range. Judge whether or not. Here, the predetermined range is a range in which it is recognized that the density D3 matches the density D4 within this range. The determination result that “difference (D3−D4) is larger than the upper limit value of the predetermined range” corresponds to the determination result that “density D3 is greater than density D4”. The determination result that “difference (D3−D4) is a value within a predetermined range” corresponds to the determination result that “density D3 is a value that matches density D4”. The determination result that “difference (D3−D4) is smaller than the lower limit value of the predetermined range” corresponds to the determination result that “density D3 is smaller than density D4”.

  Thereafter, the control unit 7 corrects the transfer conditions by the primary transfer roller 15 as necessary based on the comparison result in step S210 (steps S205 and S206). Specifically, when it becomes necessary to adjust the density distribution of the dot lines as a result of the comparison in step S210, the control unit 7 corrects the transfer bias and the transfer pressure of the primary transfer roller 15. More specifically, it is as follows.

  When the comparison result “Density D3 is greater than density D4 (D3> D4)” is obtained in step S210, the control unit 7 increases the transfer bias so that the dot line density is uniform. (Step S205). Thereafter, the control unit 7 returns to step S201.

  On the other hand, when the comparison result “Density D3 is smaller than density D4 (D3 <D4)” is obtained in step S210, the control unit 7 transfers the transfer pressure so that the dot line density is uniform. Is reduced (step S206). Thereafter, the control unit 7 returns to step S201.

  When a comparison result with “Density D3 is a value matching D4 (D3 = D4)” is obtained in step S210, the control unit 7 corrects the density distribution without changing the transfer bias and the transfer pressure. The process ends, and the process proceeds to gradation correction processing.

  According to the density distribution correction process, the density distribution of single dots or dot lines is corrected, so that the reproducibility of those density distributions is improved. Therefore, the reproducibility of the change in the density of each color is enhanced when forming a test pattern used for tone correction. Therefore, according to the image forming apparatus of the second embodiment, gradation correction can be performed with high accuracy.

  Note that the processing of steps S201 to S206 and the processing of steps S207 to S210, S205, and S206 are not limited to the case where both are executed as in the present embodiment, but only one of the processing is the density distribution correction. It may be executed as a process. Here, when the processes of steps S207 to S210, S205, and S206 are executed independently, the control unit 7 returns to step S207 after executing each of steps S205 and S206.

  In addition, by using a plurality of single dots or dot lines as a test image, an average value of densities obtained from a plurality of single dots or dot lines is used as a density to be compared in the density comparison in steps S204 and S210. be able to. This makes it possible to perform density distribution correction processing in consideration of density variations.

[3] Third Embodiment The control unit 7 may execute edge shape correction processing instead of size correction processing and density distribution correction processing in order to enable gradation correction processing with high accuracy. Details of the edge shape correction process will be described below with reference to FIG. As described in the sixth embodiment, the edge shape correction process may be used in combination with the size correction process and the density distribution correction process described above.

  In steps S301 and S302, the same processing as that in steps S101 and S102 of the first embodiment is executed. After step S302, the control unit 7 detects a single dot edge shape from the acquired image data (step S303). Specifically, the control unit 7 extracts a pixel (edge pixel) constituting an edge of a single dot from the image data, and based on the extracted edge pixel, a disturbance value V1 representing a disturbance of the edge shape. Is calculated.

  As an example, the control unit 7 calculates the barycentric coordinates from the coordinates of the edge pixels in the two-dimensional coordinate system set in the image data, and calculates the distance from the barycentric coordinates to the coordinates of each edge pixel. And the control part 7 calculates | requires the standard deviation showing the variation of the calculated distance as the disturbance value V1.

  After step S303, the control unit 7 determines whether or not the turbulence value V1 is greater than the predetermined value Vt1 (step S304). Here, the predetermined value Vt1 is an upper limit value of the turbulence value V1 that is recognized as an appropriate shape (circular shape) if the predetermined value Vt1 is equal to or less than the value. The data of the predetermined value Vt1 is stored in the storage unit 6, for example, and the control unit 7 reads the data of the predetermined value Vt1 from the storage unit 6 as necessary.

  Thereafter, the control unit 7 corrects the transfer conditions by the primary transfer roller 15 as necessary based on the determination result in step S304 (step S305). Specifically, when it is necessary to adjust the edge shape of a single dot as a result of the determination in step S304, the control unit 7 corrects the transfer bias of the primary transfer roller 15. More specifically, it is as follows.

  When the determination result that “disturbance value V1 is greater than predetermined value Vt1 (Yes)” is obtained in step S304, control unit 7 increases the transfer bias so that the edge shape of a single dot approaches a circular shape. (Step S305). Thereafter, the control unit 7 returns to Step S301.

  On the other hand, if a determination result that “the disturbance value V1 is not greater than the predetermined value Vt1 (No)” is obtained in step S304, the control unit 7 proceeds to step S306 without changing the transfer bias.

  In steps S306 and S307, the same processing as that in steps S107 and S108 of the first embodiment is executed. After step S307, the control unit 7 detects the edge shape of the dot line from the acquired image data (step S308). Specifically, the control unit 7 extracts pixels (edge pixels) constituting the edge of the dot line from the image data, and based on the extracted edge pixels, the control unit 7 calculates a disturbance value V2 representing the edge shape disturbance. calculate.

  As an example, the control unit 7 calculates the width of the dot line at each position in the extending direction of the dot line from the coordinates of the edge pixel in the two-dimensional coordinate system set in the image data. And the control part 7 calculates | requires the standard deviation showing the variation of the calculated width | variety as the disturbance value V2.

  After step S308, the control unit 7 determines whether or not the turbulence value V2 is greater than the predetermined value Vt2 (step S309). Here, the predetermined value Vt2 is an upper limit value of the turbulence value V2 that is recognized as an appropriate shape (straight line shape) if it is equal to or less than the predetermined value Vt2. The data of the predetermined value Vt2 is stored in the storage unit 6, for example, and the control unit 7 reads the data of the predetermined value Vt2 from the storage unit 6 as necessary.

  Thereafter, the control unit 7 corrects the conditions for transfer by the primary transfer roller 15 as necessary based on the determination result in step S309 (step S305). Specifically, when it becomes necessary to adjust the edge shape of the dot line as a result of the determination in step S309, the control unit 7 corrects the transfer bias of the primary transfer roller 15. More specifically, it is as follows.

  When the determination result that “disturbance value V2 is greater than predetermined value Vt2 (Yes)” is obtained in step S309, control unit 7 increases the transfer bias so that the edge shape of a single dot approaches a linear shape. (Step S305). Thereafter, the control unit 7 returns to Step S301.

  On the other hand, when the determination result that “the disturbance value V2 is not larger than the predetermined value Vt2 (No)” is obtained in step S309, the control unit 7 ends the edge shape correction process without changing the transfer bias. The process proceeds to gradation correction processing.

  According to the edge shape correction process, the edge shape of a single dot or dot line is corrected, thereby improving the reproducibility of the edge shape. Therefore, the reproducibility of the change in the density of each color is enhanced when forming a test pattern used for tone correction. Therefore, according to the image forming apparatus of the third embodiment, gradation correction can be performed with high accuracy.

  Note that the processing in steps S301 to S305 and the processing in steps S306 to S309 and S305 are not limited to the case where both are executed as in the present embodiment, but only one of the processing is executed as the edge shape correction processing. May be. Here, when the processing of steps S306 to S309 and S305 is executed independently, the control unit 7 returns to step S306 after executing step S305.

  In addition, by using a plurality of single dots or dot lines as test images, a plurality of single dots or dot lines can be used as disturbance values to be compared with the predetermined values Vt1 and Vt2 in the disturbance value comparison in steps S304 and S310. The average value of the turbulence values obtained from (1) can be used. As a result, the edge shape correction process considering the variation in the edge shape is possible.

[4] Fourth Embodiment In the first to third embodiments described above, the control unit 7 executes a scattering suppression process to suppress toner scattering that may occur when the toner image is transferred to the intermediate transfer belt 2. May be. Below, the detail of a scattering suppression process is demonstrated with reference to FIG.

  First, the control unit 7 causes each toner image forming unit 1 to form a single dot or dot line toner image as a test image (step S401). Next, the control unit 7 acquires image data of the test image by causing the imaging unit 5 to capture the formed test image (step S402).

  In the first embodiment, when the scattering suppression process is incorporated between steps S102 and S103 or between steps S108 and S109, the image data obtained in steps S102 and S109 is obtained as the image data acquired in step S402. Can be substituted. For this reason, steps S401 and S402 may be omitted. The same applies when the scattering suppression process is incorporated in the various correction processes of the second and third embodiments.

  After step S402, the control unit 7 detects from the acquired image data whether there is toner scattering traces that may occur during transfer of the test image to the intermediate transfer belt 2 (step S403). Specifically, the control unit 7 extracts the pixels constituting the image of the test image (single dot or dot line) from the image data, and the same number of pixels around the extracted pixels. It is determined whether or not there is a pixel having a value.

  When the determination result that “a pixel having the same pixel value as the extracted pixel exists” is obtained, the control unit 7 proceeds to step S404 on the assumption that the toner scattering mark has been detected. On the other hand, when the determination result that “a pixel having the same pixel value as the extracted pixel does not exist” is obtained, the control unit 7 assumes that the toner scattering trace is not detected, and performs the scattering suppression process. finish.

  In step S404, the control unit 7 corrects the transfer conditions by the primary transfer roller 15 so that the toner does not scatter during transfer (step S305). Specifically, the control unit 7 increases or decreases the transfer bias. Thereafter, the control unit 7 returns to step S401.

  According to the scattering suppression process, toner scattering that may occur during transfer of the toner image (including the test image) to the intermediate transfer belt 2 is suppressed. Therefore, in each of the size correction process (first embodiment), the density distribution correction process (second embodiment), and the edge shape correction process (third embodiment), the influence of scattering marks is removed, and as a result, it is high. Correction processing with accuracy is realized.

[5] Fifth Embodiment In the first to fourth embodiments described above, the control unit 7 controls the toner image forming unit 1 in the width direction Dw of the intermediate transfer belt 2 (a direction perpendicular to the transport direction Dt. 7), a test image may be formed at each of a plurality of different positions. In this case, the imaging unit 5 is provided corresponding to each of a plurality of positions where the test image is formed. For example, when test images are formed at positions near the front end 2a, near the center, and near the rear end 2b in the width direction Dw of the intermediate transfer belt 2, the imaging unit 5 is shown in FIG. Are provided corresponding to each of those positions.

  Then, the control unit 7 corrects the toner image forming conditions for each position by executing various correction processes using the image data of the test image at each position. Therefore, variations in the size, density distribution, edge shape, and the like of single dots and dot lines that can be caused by the difference in position in the width direction Dw of the intermediate transfer belt 2 are corrected in the image forming apparatus of the fifth embodiment.

  Different test images may be formed at a plurality of positions where the test images are formed. For example, a single dot may be formed at a position near the front end 2a and a position near the rear end 2b, and a dot line may be formed at a position near the center. Accordingly, since various correction processes for a single dot and various correction processes for a dot line can be performed in parallel, the various correction processes can be completed in a short time.

[6] Sixth Embodiment Each of the various correction processes described above may be used alone, or some or all of them may be used in combination. As an example, FIG. 8 is a flowchart showing a flow when a size correction process and a density distribution correction process are combined. As another example, FIG. 9 is a flowchart showing a flow when a size correction process and an edge shape correction process are combined. In any case, when the transfer condition by the primary transfer roller 15 is corrected (when each of steps S205, S206, and S305 is executed), the process preferably returns to step S101.

[7] Other Examples The various correction processes of the first to fifth embodiments described above may be executed at any timing in the control of the image forming apparatus. The execution timing includes, for example, a point in time when a predetermined number of prints are completed, a standby period, immediately before execution of printing, and when the image forming apparatus is activated (powered on). The various correction processes may be automatically executed under monitoring by the control unit 7, or may be displayed on a screen such as an operation panel so as to be selectable, and may be executed when any one is selected. Furthermore, when the control unit 7 determines that execution of various correction processes is necessary in order to prevent a sudden density change or the like, the process determined to be necessary is selected on the screen of the operation panel or the like. It may be displayed as possible. In this case, it is possible to cause the user to determine the necessity of executing the process.

  In the various correction processes of the first to fifth embodiments described above, the control unit 7 replaces or corrects the exposure conditions by the exposure unit 13 and the transfer conditions by the primary transfer roller 15. In addition, various toner image forming conditions in the toner image forming unit 1 such as charging conditions by the charging unit 12 and developing conditions by the developing unit 14 may be corrected.

  Since the black transfer belt is often used as the intermediate transfer belt 2, the black toner is a single dot or dot on a solid image formed using toner of a color different from black (such as yellow). A test image such as a line may be formed. As a result, the state of the test image (size, density distribution, edge shape, etc.) can be easily recognized from the image data.

  Furthermore, the state (size, density distribution, edge shape, etc.) of the test image such as a single dot or dot line is not limited to that obtained directly from the image data obtained by the imaging unit 5, but is measured by an optical sensor. It may be obtained indirectly from the reflectance of the test image. In this case, using the conventional configuration, the state of the test image can be indirectly recognized from the reflectivity and the like, and the state can be reflected in the exposure condition and the transfer condition. For example, exposure conditions and transfer conditions can be corrected from the reflectance using a density correction table or the like.

  Each component configuration of the image forming apparatus can be applied to various image forming apparatuses such as a color complex machine, a color copying machine, and a color printer. Further, the above-described configuration of each part can be applied not only to an image forming apparatus for a color image but also to an image forming apparatus for a monochrome image.

  The above description of the embodiment is to be considered in all respects as illustrative and not restrictive. The scope of the present invention is shown not by the above embodiments but by the claims. Further, the scope of the present invention is intended to include all modifications within the meaning and scope equivalent to the scope of the claims.

DESCRIPTION OF SYMBOLS 1 Toner image formation part 2 Intermediate transfer belt 5 Imaging part 7 Control part 11 Photosensitive drum 12 Charging part 13 Exposure part 14 Development part 15 Primary transfer roller

Claims (4)

An exposure unit that forms an electrostatic latent image on an image carrier, a developing unit that visualizes the electrostatic latent image to form a toner image, and a transfer roller that transfers the toner image to a transfer belt. A toner image forming unit;
An information acquisition unit that acquires optical information of the toner image after the transfer of the toner image to the transfer belt and before the toner image is fixed to paper;
A control unit;
With
The controller is
(I) causing the toner image forming unit to form at least one of a single dot toner image and a dot line toner image in which a single dot is arranged in one or more rows in a predetermined direction as a test image; A process for causing the information acquisition unit to acquire optical information of the formed test image;
(Ii) a process of correcting the toner image forming condition in the toner image forming unit based on the state of the test image obtained from the optical information acquired by the information acquiring unit;
An image forming apparatus that executes   The image forming apparatus according to claim 1, wherein the state of the test image includes at least one of a size, a density distribution, and an edge shape. The controller is
(Iii) a process of detecting the presence or absence of toner scattering marks that may occur during transfer of the test image to the transfer belt from the optical information acquired by the information acquisition unit;
(Iv) Based on the detection result in the process (iii), a process for correcting the transfer conditions by the transfer roller as necessary;
The image forming apparatus according to claim 1, further comprising: 4. The process according to claim 1, wherein in the processing (i), the control unit causes the toner image forming unit to form the test image at each of a plurality of different positions in the width direction of the transfer belt. An image forming apparatus according to claim 1,
The information acquisition unit is provided corresponding to each of the plurality of positions,
In the process (ii), the control unit corrects the toner image forming condition for each position by using optical information of the test image at each position.

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